Electric fluid heater



June 18, 1935/ R. A. CARLETON 2,004,976

ELECTRIC FLUID HEATER Filed Aug. 7, 1931 4 Sheets-Sheet 1 2 5 INVENTOR.

F--- 2 ROBERT AQCHRLETDN 1g y VM,M,7FM\ M- ATTORNEYS June 18, 1935. "R.A. CARLETON ELECTRIC FLUID HEATER 4 Sheets-Sheet 2 .Filed Aug. 7, 1951INVENTOR ROBERT A. CARLETON June 18, 1935.

R. A. CARLETON ELECTRIC FLUID HEATER Filed Aug. '7, 1931 4 Sheets-Sheet3 INVENTOR. Ross/w A. CARLETON BY Flg. 6..

ATTORNEYS June 18, 1935. R. A. CARLETON ELECTRIC FLUID HEATER Filed Aug.7, 1931 4 Sheets-Sheet 4 Fig. 10.

L78 75 ay AV/JF/AY/AIV/AV/AV/AV/AM Fig. 9.

&N mw V mm C A m E w R BY M M hfm 77M A TTORNEYS Patented June 18, 1935i UNITED STATES PATENT OFFICE ELECTRIC FLUID HEATER Robert A. Carleton,Brooklyn, N. Y., assignor to National Electric Heating Company, Inc.,New York, N. Y., a corporation of New Jersey Application August 7, 1931,Serial No. 555,801

8 Claims. (Cl. 219-38) This invention relates to improvements inelecalso been found desirable to incorporate a safety tric fluid heatingapparatus of the type in which switch which will stop the flow ofcurrent to the the fluid is heated by direct contact with the heatingunits in case the amount offluid in the heating elements. heater dropsbelow a predetermined minimum.

In electric heaters great difliculty has been In constructing theheater, it has been found 6 encountered in obtaining rapid heating andthe that non-corrosive metals may very advantaheaters heretofore usedhave been of low eiilgeously be employed to prevent the fluid beingciency and rather prone to get out of order and treated from damagingthe heater. When so need adjustment and repairs. constructed there ispractically nothing in the The object of this invention is therefore toprodevice which is subject to deterioration or break- 10 vide anelectric fluid heater which will operate age or which is liable to getout of adjustment. both rapidly and efliciently and which is of a Itwill thus be apparent that the heater as consufliciently ruggedconstruction so that it will not structed according to this inventionwill possess easily get out of order. all those qualities of efliciency,durability, speed It is the further object of this invention to andautomatic control which are desirable. 15 provide' a heater of this typewhich will operate For a more detailed description of the apparaeitheron direct current or on alternating curtus of this invention, referencemay be had to rent having any of the usual characteristics and theappended drawings and the description which will be adaptable for bothdomestic and thereof.

industrial use. In the drawings, Figure 1 is a plan view in 20 Withthese objects in mind, heating elements section of the apparatus. havebeen devised which have the form of thin, Figure 2 is an elevationalview of the heater .closely -spaced ribbons of metal having a high insection taken on the line 2-2 of Figure 1 and electrir'al resistance,and a plurality of these elethis view shows the electrical connectionsto ments are held edgewise between supports to form the heater. 25heating units. A series of these heating units are Figure 3 is anenlarged sectional elevation of mounted for use in parallel relation andelectrithe heater units. cally connected so that the current flowsthrough Figure 4 is a detailed sectional view of a part the alternateunits in opposite directions. The of the heater units showing the methodof supheater is swported within a tank where the fluid porting theribbons; and 30 is caused to circulate between the closely spaced Figure5 is a P View Of the Section hown ribbons from which it is heated. inFigure 4.

By the closely spaced, thin ribbon between Figurefi is a sectionalelevation of a circulatwhich the fluid is caused to flow a very highrate ing fluid hea er embody n the p pl f his of heat transfer isaccomplished and large nv 35 amount of current may be passed through theFigure 7 is a sectional view of the deviceshown heating elements andrapid heating of the fluid in Figure taken o h l ne 1. may take place.By arranging the units which Figure 8 is a sectional view of the devicemake up the heater so that the current flows in Shown in Figure 6 takenon e e ll8.

4U opposite directions through adjacent units the Figures 9 and 10 aresectional detail views Of self-induction in the heating units isneutralized the d ce of Figure 6 on an enlar d Scaleand the power factorand hence the efiiciency of As illustrated in Figu es 1 to 5 0f thedrawthe device greatly increased. By clamping the 8 011601? t ePreferred Constructions p ythin ribbons edgewise between supports, theyare ing the principles of this invention is a fluid held rigidly inposition and this coupled with the heater in which the fluid iscirculated through 5 structure which will be further described pro theheater by the convection currents set up by duces an electric fluidheater which is excepthe heating units. The heater comprises a tanktionally rugged and has little tendency to get out made up of aninner-shell 2| Su p d d Wi n of order or need adjustment. an outer shell22 and insulated therefrom by In order that the temperature to which theinsulating material 23. The inner shell is prei- 50 fluid is heated maybe accurately controlled, it has erably of some non-corrosive metal suchas been found desirable to control the amount of Monel metal, copper, orthe like; while the outer current which flows through the heatingelements shell 22 is usually of sheet steel. The insulating by use of athermostat operated in accordance material may be any of the well knownmatewith the temperature of the heated fluid. It has rials such asasbestos, diatomaceous earth, mineral wool or the like. The fiuid entersthe tank through an inlet 24 and leaves through an outlet 25. The top ofthe tank is open but is covered by a hood 26 from which fumes and vaporsare exhausted through an outlet 21.

A heating device 28 is suspended within the tank near the bottom thereofby means of metal strips 29 which are supported from a ring 30 near thetop of the tank. The ring; 30 is received in slots in lugs 3i which arewelded or otherwise suitably fastened to the inner wall of the tank nearthe top, thereof. Bolts 32 hold the ring 30 tightly in place.

The heating device comprises a plurality of heating units eachconsisting of a thin metal rib bon formed into a closely sp'aced'spiral33. The

spirals 33 are secured rigidly in place by being I clamped edgewisebetween radially extending insulating plates 34. Each of the insulatingplates 34 is provided with a plurality of grooves 35 which receive theedges of the spiral ribbons. The radial insulating plates 34 may be ofany suitable insulating material such as slate orporcelain. The outerinsulating plates have grooves only onv their inner edges but theinsulating plates between adjacent spirals of metal ribbon have grooveson the opposite edges and the as sistance of supporting two of thespirals.

The insulating plates 34 are supported by radially extending arms 35 towhich they are attached by the bolts 31. The radial extending arms 36areall secured to a frame member 38 I which extends axially of thespirals at the center thereof. Bolts 39 are used to secure the radialarms 36 to the frame member 38.

. Each groupof parallel radial arms 38 are secured together at theirouter ends by a bar 40 to which they are bolted by the bolts 4|. bars 40are parallel to the frame member 38 and are all attached at theirupperends to a ringshaped strip 42 by means of angle brackets 43 which arebolted to the bars 40 by bolts 4! which secure the radial arms to thebars 40 and bolts 44 by which the angle brackets are fastened to thering 42. The bottom ends of the bars 40 are similarly connected to aring-shaped strip 45 and the ring-shaped strips 42 and 45 are 1nv turnbolted or otherwise suitably connected to the supporting strips 29.

The inner ends of the spirals 33 are all connected together by aconnector strip 46, and the outer ends of the spirals are eachseparately connected to the source of current supply. These connectionsare made by meansof connecting strips which connect detachably toconnecting strips 5| at a connection block 52 which is supportedadjacent the units by a supporting member 53 suitably attached to therings 42 and 45. The connecting strips 5| connect to insulatedconnecting ,bolts' 49 which extend through insulated and oil tightbushings in the tank wall. Current is supplied to the connecting bolts49 outside of the, tank to energize the heating units. i

In the device shown, there are three heating units and the heater isoperated on a three-phase The ' device,

of the switches. Current to operate the magnetic switches is taken fromthe main line below the main switch 55 by a pair of wires and 60a. Thewires 50 and 60a are connected to a. hand operated switch 6! which maybreak the circuit and thereby allow the magnetic switches to open andthe main circuit to be broken. From the hand operated switch 6| thewires60'lead to a. float operated switch 62 which has a float 52' inside thetank and operates to break the circuit if the fluid level in the tankfalls below a predetermined minimum. From this switch the wire 60 leadsto a thermostat switch 53 which has a heat sensitive element 64extending into the tank and which'operates to break the circuit if thetemperature in the tank exceeds a predetermined maximum. From thisswitch the wire 60 leads to a thermostatic control switch 55 having aheat sensitive element 56 extending into the tank. and operating toselectively connect the wire 50 to either the wire 61 which leads to themagnet of the switch 56 or the wire 68 which leads to the magnet of theswitch 58. The thermostatic control switch 55 operates so that it opensthe switch 55 and closes the switch 58 when the temperature reaches apredetermined maximum and reverses the operation when the temperaturereaches a predetermined minimum. thus tending to keep the fluid ture.

In the circulating fluid heater as illustrated in Figures 6 to 10, thedevice comprises a tank 10 preferably of non-corrosive metal surroundedby a casing ll of sheet metal or the like and having insulation material12 between the tank and the sheet metal casing. The tank is providedwith an inlet 13 and'an outlet 74 and isclosed both at the top and atthe bottom so that liquid may be forced to circulate therethrough underthe pressure of a pump or similar circulating As in Figures 1 to 6, theheating units 33 are in the form of closely spaced spirals of metalribbon held edgewise between radially ex tending insulating plates 34which are in turn bolted to radially extending supporting arms.

A frame '15 having radially extending supporting arms 76 is mounted .ona rod 11 which extends axially of the spirals, the insulating plates 34are fastened to the radially extending arms by means of bolts 13 and theframes 15 are spaced along the rod 1'! by means of collars 19 whichsurround the shaft 11 between the frames. The ends of the rod 11 arethreaded to receive'nuts 79 which hold the framesin a spaced positionupon the rod. The block 80 is bolted to the outer end of each 'of theradial arms 16 and rods 8| extend through the blocks 80 and aresurrounded by collars 82 which space the blocks along the rod. Each ofthe rods 80 is also threaded-at its ends to receive nuts 83 which holdthe blocks and collars in position thereon.

A flatring 85 lies on top of each set of blocks which are in the samehorizontal plane and prevents the flow of fluid around the sides of theheating units. The rings 85'are cut out to surround the rods 8! and areclamped between the collars 82 and the blocks 80. Perforated plates 86lie both above and below the heating device and are held in place bymeans of supporting strips suitably fastened thereto as by welding.

fit around in the tank at a fixed tempera- (ill by means of brackets 90which are held on the top of the rods 80 by the nuts 83 and bolted tothe sides of the tank 10 by bolts 9i.

Conducting strips 93 connect to the outer ends of a part of the spiralsand connecting strips 94 connect the inner ends of a partof the spiralstogether. The connecting strips 93 extend through spacers 95 supportedfrom the radially extending supporting arms and are suitably insulatedtherefrom by insulators 96. These connecting strips 92 connect withinsulated bolts 91 which passthrough the wall of the tank and areconnected on the outside with a suitable source of electric current.

As shown in the drawings, the connections 93 and 94 are so arranged thatthe heating spirals are connected in three series of four spirals each,and each of the series is connected across one phase of a three-phasealternating current which is supplied from a supply line 98 through amagnetic switch 99.

The magnetic switch 99 is controlled by a circuit I00 which receives itspower from the main supply line 98 and may be broken by either athermostatic switch l0! operated by a heat sensitive element I02 nearthe outlet of the heater or by a switch I03 which is connected to theintake of the heater and operates to break the circuit upon substantialcessation of the flow of fluidto the heater. This circuit may also bebroken by a hand operated switch I04 and when broken by any of theseswitches the magnetic switch is opened to stop the flow of current tothe heater. This prevents the flow of current to the heater when thefluid in the heater becomes too hot or ceases to flow and thus preventsdamage to the fluid or the heater.

It will be apparent from the foregoing description that the fluidflowing through the heater will be caused to flow through the relativelysmall spaces between the metallic ribbons and will thus be subjected tothe heating effect of a large, surface over which the fluid will pass inrelatively small streams.

It may also be "observed that the heating elements being of lightmaterial and in direct contact with the liquid'will cool quickly'if thecurrent is shut off and the apparatus may therefore be very finelycontrolled to give a very accurate temperature adjustment.

The apparatus of this invention is useful for any kind of fluid heating,but the apparatus of Figures 1 to'6 is particularly adapted to heatingand bodying or polymerizing linseed or similar oils. When bodyingsuch'oils, the oil is heated to a selected temperature usually withinthe range of 560 to 625 F and maintained at the selected temperature fora period of time necessary for the desired bodying or polymerizing reaction to take place which may require from one to tenhours or more,depending upon the kind or quality of the oil, the temperature at whichit is treated and the body or viscosity required.

When heated to a certain temperature, which may vary with differentoils, but is usually between 560 to 575 F. an exothermic reaction takesplace within the oil, causing a relatively rapid rise in temperature,the degree and rate of tem perature rise depending somewhat upon therate or speed the oil has been heated, the slower the rate of heat inputat the critical temperature, the less the temperature rise due to theexothermic reaction.

When the oil is heated to or near its critical or reaction temperature,a relatively slight increase in temperature will cause cracking orbreakdown of the oil molecules to take place. converting part of the oilinto free fatty acids. carbon and other compounds that injiu'iousiyeffect the quality of the finished oil and reduces its value for thepurpose intended. It is therefore very important that the heatingapparatus in which the oil is' heated be closely controlled and quicklyrespon sire to changes in temperature of the oil.

In usual constructions. theoil'isheated in open portable kettles of oneto two hundred gallon capacity. wheeled over open fires of coal or coke.and the usual means of controlling the temperature of the oil is for theattendant to withdraw the kettle from the fire should the oil becometoo.

not and replace the kettle as it becomes too cool. under whichconditions the temperature regulation is poor. the temperature of theoil varying in some instances 30] F. or more. Larger size kettles aresometimes used. in which event they are installed permanently in bricksettings and heated by means of coke or oil fires.

During the heating operation the layer of oil in contact with the kettlebottom, the underside of which is exposed to a furnace combustion temiperature of 2400" F. or more, is overheated and cracked or decomposed,increasing the loss due to oil fumes and vapors. increasing the fattyacid content and causing darkening of the oil.

As stated. it is desirable to heat the oil in a regular and uniformmanner,. avoiding the use of highly heated surfaces, and tomaintain theoil at a regular and uniform temperature throughout the period of timerequired to obtain the desired bodying reaction.

In the apparatus illustrated in Figures 1 and 2. the heating elementscomprising the relatively thin ribbons closely spaced apart in the formof concentric spirals, presents the greatest possible heating surfacearea, uniformly distributed in the fluid in the receptatcle. and due tothe thermosiphonic action of the hot oil rising through and between andin direct contact with the heating surfaces comprising the spirals ofthe heating element,creates a vigorous circulation, providing themaximum heat transferrate and the minimum temperature differentialbetween the heating surfaces and the oil in contact therewith.

Due to the relatively small mass or weight of the high resistancemetallic ribbons comprising the heating elements, and the relativelysmall temperature differential between the heating sur faces and theoil, the amount of heat stored in the heating elements and given offafter the ele tric heating current is interrupted is negligible. 5

in I

lit)

the heating surfaces. Of the three main conditions influencing the rateofheat absorption. the second and third are the more important.following example will illustrate the advantage of the arrangement ofthe heating element as shown in Figures 1 and 2, of the presentinvention.

Assuming a 1000 gallon oil fired oil bodying The the close spacing ofthe kettle, having a diameter of 66 inches and'a height of .110 inches,the oil filling the kettle to a height of 66 inches from the bottom, theheat being applied to the kettle bottom and for a distance of 12 inchesup the sides, providing a total area. of 5840 square inches of heatingsurface. The heat must'be transmitted from the bottom and lower sides ofthe kettle inches.

The heater which is the subject or this inventhe vertical spacing oftheheating elements presenting both sides of the ribbons as the heatingsurfaces with which the oil is in direct contact, there is a vigorouscirculation of the oil created up through the said spirals and down thesides 'of the kettle between the outer turns of the walls of the kettle,which spirals and the side readily absorbs the heat generated in theheatingelements, tending to cool them and permitting the use of arelatively high rate of heat input per unit area of heating surface.

The greater rate of -heat absorption, due to heating elements or spiralsof high resistance ribbons, as compared to the direct fired kettleheated by oil mentioned above is illustrated by the following example;

Heating speed ratio.

Electrica y hcflted -".375

, 11,37s fired kCttlC Q or the electrically heated kettle, due to theclose spacing and arrangement of the heating surfaces will have a.heating speed, other conditions being equal, 11,378 times that of theoil fired kettle.

Heating surface ratio Electrically heated kettle 49,500 square inchesOil fired kettlc Q s 5,840 square inches or the electrically heatedkettle by reason of the greater area of heating surface exposed, willhave a heating-speed 8.5 times that of the oil fired kettle, or theelectric kettle may be operated at the same speed as the oil firedkettle, but-at a temperature-difference between heating surface and oilof but 11.8% that of the oil firedkettle. The above heating speed andheating surface ratios may be readily increased to anydesired degree byreducing the distance between adjacent'turns of the spirals, and using agreater length of, or by increasing the width of the high resistanceribbons, thereby increasing the area of the heating surface. I

Due to the arrangement. of the heating surfacesin the electricallyheated kettle, which creates a vigorous circulation of the oil uniformlythrough the spirals comprising the heating elements, the velocity flowof the oil in contact with the said heating surfaces, will, theviscosity of the oil, be from 10 to times greater than in the oil firedkettle using the botto the centre of the mass of oil, or to a distanceof approximately ing elements comprising the to a polyphase electric tomand lower sides only as the heating surface. In the operation of thekettle, the oil being placed in the receptacle, the push button switch 6is closed, causing the magnetic switch56 tov close and the electricheating current to pass by means of the main switch 55, the magneticswitch 56 and electrical connections to the electric heatribbons 33 ofhigh resistance metal, causing heat to be generated therein andtransmitted to the oil that is in direct contact therewith. The oilcirculatingvigorously upwardly through the spirals comprising theheating elements and down the space between the outer edge of thespirals and the sides of the kettle, iS quickly and uniformly heated tothe desired degree.

If it is assumed that 1000 gallons of linseed is to be heated from atemperature of 60 F. to 585 F. and maintained thereat for a period offour hours to attain the desired viscosity, that at 560 an exothermicreaction occurs in the oil, causing a temperature rise of 20, that thereis required an electrical input at the rate of 300 kw. for 2 hours toraise the oil from-60 to 560, that the electric energy required tosupply radiation losses and maintain the oil at .585" is at the rate of8 kw.' Therefore the thermostatic control switch 65 is set at 560 andwhen the temperature of the oil reachis that degree, thermostat willthen act to open the magnetic switch 56 and to close the magnetic switch58, the electric heating current then passing by'means of theauto-transformer 51 or other suitable electric power reducing device, byway of the magnetic switch 58 'to the heating elements in the kettle,being reduced by means of the auto-transformer to an electric capacityof slightly more than that required to maintain the oil at 585 orlO kw.Due to the exothermic reaction mentioned above, the tem perature of theoil will continue to rise to 585, whereupon the thermostatic switch 63will act to open the control circuit, causing the magnetic switch 58 toopenand interrupt the electric heating current supplied'resistanceelements. Should the temperature of the oil become less than 585,thermostatic switch 63 will act, causing magnetic switch 58 to close andsupply the electric heating current to the heating elements, thus actingto maintain the oil in receptacle, accurately, at a determinate degreeof heat.

It is desirablethat the control system used to regulate the electriccurrent supplied heating elements be so. arranged as to avoid thefrequent turning on and off of relatively large electric currents thatmay cause disturbance to the electric power supply system. In thepreferred method of control hereinbefore described-the high electriocapacity current of 300 kw. is turned on at the start .of the heatingperiod, and after the oil' is heated to the desired temperature, thehigh through heating elements at all times except when they a. .3immersed to a predetermined degree in the oil, so that accidentaloverheating oi the heating elements is avoided.

It will be obvious that many other embodiments of the invention may bemade by those skilled in the art and it will therefore be understoodthat theparticular devices and arrangements and methods of use shown anddescribed herein are of an illustrative character and are notrestrictive and that various changes in form, construction andarrangement of parts may be made within the spirit and scope of theiollowing claims and such suitable electric current may be employedwhether direct, single, or polyphase alternating, as may be availableand adapted to the particular requirement of the apparatus used.

Having thus described the invention, what I claim is:

1. In a fluid heating apparatus, the combination of a receptacle forcontaining the fluid, a heating element consisting of a long narrowribbon of high electrical resistance material wound in a spiral having adiameter substantially greater than its width, means supporting theelement substantially horizontally in the receptacle, and a source ofelectrical heating current connected to the element for heating thesame.

2. In afluid heating apparatus, the combination of a receptacle forcontaining the fluid, a plurality of heating elements each consisting ofa long narrow ribbon of high electrical resistance material wound in aspiral having a diameter substantially greater-than its width, meanssupporting said elements substantially horizontally in the receptacle invertically spaced relation, and a' source of electrical heating currentconnected to said elements for heating the same.

3. In a fluid heating apparatus, the combination of a receptacle forcontaining the fluid, a heating element consisting, oi a long narrowribbon of high electrical resistance material wound in a spiralhaving adiameter substantially greater than its width, means supporting theelement substantially horizontally in the receptacle, a source ofelectrical heating current connected to the element for heating thesame, and means maintaining the level of the fluid in the receptaclesubstantially above'the top of said element to insure thermosiphoniccirculation of the fluid over both surfaces of the ribbon.

4. In a fluid heating apparatus, the combination of a receptacle forcontaining the fluid, a plurality of heating elements each consisting ofa long narrow ribbon of high electrical resistance ,material wound in aspiral having a diameter substantially greater than its width, meanssupporting said elements substantially horizontally in the receptacle invertically spaced relation, a source of electrical heating currentconnected to said elements for heating the same, and means maintainingthe level of the fluid in the receptacle above the upper element toinsure thermosiphonic circulation oi! the fluid over both surfaces ofthe ribbon.

5. A fluid heating apparatus comprising a fluid containing receptacle, aplurality of electric heating elements comprising thin ribbons of highelectrical resistance metal, edge supported in a closely spaced spiralform, in said receptacle and immersed in said fluid, means to cause thefluid to flow in a predetermined direction between said elements and indirect contact therewith, means for passing an electric heating currentthrough said high resistance metallic ribbons, thermostatic meanssubject to the temperature oi the fluid to selectively controlthemagnitude of the electric heating current passed through said heatingelements, and thermostatic means subject to the influence of thetemperature of the fluid to automatically control the supply of electriccurrent to said electric heating elements.

6. A fluid heating apparatus comprising a fluid containing receptacle, aplurality or superimposed electric heating elements comprising thinribbons of high electrical resistance metal, wound in a closely spacedspiral form, means supporting said elements in superposed spacedrelation in said receptacle and immersed in said fluid, means to causethe fluid to flow in a predetermined direction between said elements andin direct contact therewith, means for passing an electric heatingcurrent through said high resistance metallic ribbons, and automaticmeans operable by a predetermined minimum height of the fluid withinsaid receptacle to disconnect the supply of electric current to saidelements.

'7. A fluid heating apparatus comprising a fluid containing receptacle,a plurality of electric heating elements comprising thin ribbons of highelectrical resistance metal, edge supported in a closely spacedhorizontal spiral form, in said receptacle and immersed in said fluid,means to cause the fluid to flow in a predetermined direction betweensaid elements and in direct contact therewith, means for passingan'electric heating current through said high resistance metallicribbons, thermostatic means subject to the temperature of the fluid toselectively control the magnitude 0! the electric heating current passedthrough said heating elements, thermostatic means subject to theinfluence oi the temperature of the fluid to automatically control thesupply of electric current to said electric heating elements andautomatic means operable by the height or the fluid within saidreceptacle to con- .trol the supply of electric current to saidelements.

8. A fluid heating apparatus comprising a fluid containing receptacle,having an inlet and an outlet, a plurality of electric heating elementscomprising closely spaced spirals of relatively narrow metallic ribbonsof high electrical resistance wound in spiral form, means supportingsaid elements transversely, one above the other within said receptacleandimmersed in said fluid, means for passing an electric heating currentthrough saidhigh resistance metallic ribbons, means for causing thefluid to flow uniformly between said heating elements and in directcontact therewith.

ROBERT A. CARLETON.

